1. Field of the Invention
The present invention relates to a piezoelectric vibrator and, more particularly, to a piezoelectric vibrator used for a vibrating gyroscope for detecting a rotational angular velocity.
2. Description of the Prior Art
FIG. 5 is a perspective view showing an example of a vibrating gyroscope using a conventional piezoelectric vibrator, and FIG. 6 is a sectional view of it. A vibrating gyroscope 1 includes a piezoelectric vibrator 2. The piezoelectric vibrator 2 includes a vibrating body 3 having, for example, a regular triangular prism shape. Piezoelectric elements 4a, 4b and 4c are formed respectively to three side faces of the vibrating body 3. A ridge line of the vibrating body 3 is supported at two portions in the vicinity of two nodal points by supporting members 5. An oscillation circuit is connected between the piezoelectric elements 4a, 4b and the piezoelectric element 4c. The piezoelectric elements 4a and 4b are connected to a differential circuit. The differential circuit is connected to a detecting circuit, and the detecting circuit is connected to a smoothing circuit.
The vibrating body 3 makes a bending vibration in a direction perpendicular to the face of the piezoelectric element 4c by a driving signal of the oscillation circuit. When a rotational angular velocity is not applied to the vibrating gyroscope 1, the piezoelectric elements 4a and 4b bend in a same manner, and the same signals are supplied to the differential circuit. Input signals are offset in the differential circuit, and an output signal is not obtained from the differential circuit. When the vibrating gyroscope 1 rotates about the axis of the vibrating body 3, the vibrating direction of the vibrating body 3 changes due to a Coriolis force. Thus, bending conditions of the piezoelectric elements 4a and 4b are changed, and different voltages are generated in the piezoelectric elements 4a and 4b which are connected to the differential circuit. The output signal is obtained from the differential circuit, and the signal is detected by the detecting circuit and smoothed by the smoothing circuit. Since a smoothed signal corresponds to the rotational angular velocity, the rotational angular velocity applied to the vibrating gyroscope 1 is detected by measuring the smoothed signal.
When the vibrating body used for the piezoelectric vibrator 2 is manufactured, the vibrating body 3 having a regular triangular prism shape is formed by die deforming or roll deforming of a rod made of constant elastic metal material. The ridge line of the vibrating body 3 is cut for adjusting a resonance frequency of the vibrating body 3. When the width of the vibrating body 3 is shortened, the resonance frequency of the vibrating body 3 becomes low.
The ridge line supported by the supporting members 5 is pressed for obtaining a bending vibration perpendicular to the side face of the piezoelectric element 4c exactly at the time of non-rotation. As the pressing method, for example, the method of hitting the ridge line of the vibrating body 3 is adopted. When the ridge line of the vibrating body 3 is pressed, the width of the vibrating body 3 is shortened, and the density of the vibrating body 3 is enlarged, resulting in high hardness of the ridge line portion. It has been known that the resonance frequency of the vibrating body 3 becomes high when the hardness becomes high. Thus, the lowering of the resonance frequency due to the shortening of width of the vibrating body 3 and the upwardness of the resonance frequency due to the upwardness of hardness of the vibrating body 3 are offset, and resulting in unchanged resonance frequency. The anisotropy is generated in vibrating tendency of the vibrating body by making difference of the hardness different between one ridge line and the other two ridge lines, and the bending vibration can be made to the vibrating body 3 in a direction perpendicular to the side face of the piezoelectric element 4c exactly. Therefore, the vibrating gyroscope 1 having preferable drift characteristics can be obtained.
However, when the method of pressing one ridge line of the vibrating body is adopted, there is a vibrating body having unstable bending vibration, and resulting in undesirable drift characteristics. There is a method that the hardness of each ridge line portions of the vibrating body is measured firstly, and one ridge line to be pressed is selected for obtaining the piezoelectric vibrator having preferable drift characteristics. However, it is difficult to select the ridge line to be pressed.